N = 100000;
A = 0.5.*rand(3,M);
a1 = sqrt(sum(A.*A))<0.5;
A(1,:)=A(1,:).*a1;
A(2,:)=A(2,:).*a1;
a2 = sqrt(A(1,:).^2+A(2,:).^2)>0.3;
sum(a2)/N;
